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Abstract:

A power source comprised of a first battery pack (e.g., a non-metal-air
battery pack) and a second battery pack (e.g., a metal-air battery pack)
is provided, wherein the second battery pack is used when the user
selects an extended range mode of operation. Minimizing use of the second
battery pack prevents it from undergoing unnecessary, and potentially
lifetime limiting, charge cycles.

Claims:

1. A method of extending driving range of an electric vehicle, the
electric vehicle including at least a first battery pack and a second
battery pack, wherein the first and second battery packs are comprised of
different battery types, the method comprising the steps of: providing
means for selecting between a normal mode of operation and an extended
range mode of operation; wherein when said extended range mode of
operation is selected, the method further comprises the steps of
supplying vehicle operational power to the electric vehicle from the
first battery pack and from the second battery pack; and wherein when
said normal mode of operation is selected, the method further comprises
the steps of supplying vehicle operational power to the electric vehicle
from the first battery pack and not from the second battery pack.

2. The method of claim 1, wherein said first battery pack is comprised of
a plurality of non-metal-air cells and said second battery pack is
comprised of a plurality of metal-air cells.

3. The method of claim 1, wherein said means for selecting between said
normal mode of operation and said extended range mode of operation is
integrated within a user interface corresponding to said electric
vehicle.

4. The method of claim 1, wherein said means for selecting between said
normal mode of operation and said extended range mode of operation is
integrated within a navigation system corresponding to said electric
vehicle.

5. The method of claim 1, wherein when said normal mode of operation is
selected, the method further comprises the steps: a) determining a
current state-of-charge (SOC) of the first battery pack; b) comparing
said current SOC of the first battery pack with a first preset minimum
SOC, wherein if said current SOC of the first battery pack is greater
than said first preset minimum SOC said method returns to step a), and
wherein if said current SOC of the first battery pack is less than said
first preset minimum SOC said method further comprises the step of: c)
supplying vehicle operational power to the electric vehicle from both the
first battery pack and the second battery pack.

6. The method of claim 5, wherein prior to step b) said method further
comprises the steps of: a2) comparing said current SOC of the first
battery pack with a second preset minimum SOC, wherein said first preset
minimum SOC is greater than said second preset minimum SOC, wherein if
said current SOC of the first battery pack is less than said second
preset minimum SOC said method skips to step c), and wherein if said
current SOC of the first battery pack is greater than said second preset
minimum SOC said method performs step b).

7. The method of claim 5, wherein prior to step c) said method further
comprises the steps of: b2) determining a current SOC of the second
battery pack; b3) comparing said current SOC of the second battery pack
with a second preset minimum SOC, wherein if said current SOC of the
second battery pack is greater than said second preset minimum SOC said
method continues to step c), and wherein if said current SOC of the
second battery pack is less than said second preset minimum SOC said
method further comprises the steps of: i) comparing said current SOC of
the first battery pack with a second preset minimum SOC, wherein said
first preset minimum SOC is greater than said second preset minimum SOC,
wherein if said current SOC of the first battery pack is greater than
said second preset minimum SOC said method returns to step a), and
wherein if said current SOC of the first battery pack is less than said
second preset minimum SOC said method further comprises the step of
terminating vehicle operation.

8. The method of claim 1, wherein when said extended range mode of
operation is selected, the method further comprises the steps: a)
determining a current SOC of the second battery pack; b) comparing said
current SOC of the second battery pack with a first preset minimum SOC,
wherein if said current SOC of the second battery pack is greater than
said first preset minimum SOC, charging of the first battery pack by the
second battery pack continues, and wherein if said current SOC of the
second battery pack is less than said first preset minimum SOC said
method further comprises the steps of: c) terminating use of the second
battery pack to supply vehicle operational power to the electric vehicle;
d) determining a current SOC of the first battery pack; e) comparing said
current SOC of the first battery pack with a second preset minimum SOC,
wherein if said current SOC of the first battery pack is greater than
said second preset minimum SOC said method returns to step a), and
wherein if said current SOC of the first battery pack is less than said
second preset minimum SOC said method further comprises the step of
terminating vehicle operation.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of U.S. patent application Ser.
No. 12/962,851, filed Dec. 8, 2010, which is a continuation of U.S.
patent application Ser. No. 12/962,693, filed Dec. 8, 2010, which claims
benefit of the filing date of U.S. Provisional Patent Application Ser.
No. 61/372,351, filed Aug. 10, 2010, the disclosures of which are
incorporated herein by reference for any and all purposes.

FIELD OF THE INVENTION

[0002] The present invention relates generally to batteries and, more
particularly, to means for optimizing the power source of an electric
vehicle that utilizes battery packs of differing types.

BACKGROUND OF THE INVENTION

[0003] A metal-air cell is a type of battery that utilizes the same energy
storage principles as a more conventional cell such as a lithium ion,
nickel metal hydride, nickel cadmium, or other cell type. Unlike such
conventional cells, however, a metal-air cell utilizes oxygen as one of
the electrodes, typically passing the oxygen through a porous metal
electrode. The exact nature of the reaction that occurs in a metal-air
battery depends upon the metal used in the anode and the composition of
the electrolyte. Exemplary metals used in the construction of the anode
include zinc, aluminum, magnesium, iron, lithium and vanadium. The
cathode in such cells is typically fabricated from a porous structure
with the necessary catalytic properties for the oxygen reaction. A
suitable electrolyte, such as potassium hydroxide in the case of a
zinc-air battery, provides the necessary ionic conductivity between the
electrodes while a separator prevents short circuits between the battery
electrodes.

[0004] Due to the use of oxygen as one of the reactants, metal-air cells
have some rather unique properties. For example, since the oxygen does
not need to be packaged within the cell, a metal-air cell typically
exhibits a much higher capacity-to-volume, or capacity-to-weight, ratio
than other cell types making them an ideal candidate for weight sensitive
applications or those requiring high energy densities.

[0005] While metal-air cells offer a number of advantages over a
conventional rechargeable battery, most notably their extremely high
energy density, such cells also have a number of drawbacks. For example,
care must be taken to avoid the undesired evaporation of electrolyte,
especially in high temperature, low humidity environments. It is also
necessary to ensure that there is a sufficient supply of air to the cells
during discharge cycles, and means for handling the oxygen emitted from
the cells during the charge cycles. Another potential disadvantage of a
metal-air cell is the power available on discharge. Due to the kinetics
of the electrode reactions, the maximum discharge rate is far lower than
that of many other types of cells, such as lithium-ion cells.

[0006] Accordingly, while metal-air cells offer some intriguing benefits,
such as their high energy densities, their shortcomings must be taken
into account in order to successfully integrate the cells into a system.
The present invention provides such a system by combining a metal-air
battery pack with a conventional battery pack in order to gain the
benefits associated with each battery type.

SUMMARY OF THE INVENTION

[0007] The present invention provides a power source comprised of a first
battery pack (e.g., a non-metal-air battery pack) and a second battery
pack (e.g., a metal-air battery pack), wherein the second battery pack is
only used as required by the state-of-charge (SOC) of the first battery
pack or as a result of the user selecting an extended range mode of
operation. Minimizing use of the second battery pack prevents it from
undergoing unnecessary, and potentially lifetime limiting, charge cycles.
The second battery pack may be used to charge the first battery pack or
used in combination with the first battery pack to supply operational
power to the electric vehicle.

[0008] In at least one embodiment of the invention, a method of extending
driving range of an electric vehicle is provided, the electric vehicle
including at least a first battery pack (e.g., non-metal-air battery
pack) and a second battery pack (e.g., metal-air battery pack), the
method including the steps of providing means for selecting between a
normal mode of operation and an extended range mode of operation, wherein
when the extended range mode is selected vehicle operational power is
provided by both the first battery pack and the second battery pack, and
wherein when the normal mode is selected vehicle operational power is
only provided by the first battery pack. The means for selecting between
modes may be integrated within the vehicle's user interface or navigation
system. When the normal mode of operation is selected, the method may
further include the steps of (i) determining the SOC of the first battery
pack; and (ii) comparing the current SOC of the first battery pack to a
first preset minimum SOC, wherein if the current SOC of the first battery
pack is greater than the first preset minimum SOC, vehicle operational
power continues to be supplied by only the first battery pack, and
wherein if the current SOC of the first battery pack is less than the
first preset minimum SOC, vehicle operational power is supplied by both
the first and second battery packs. When the normal mode of operation is
selected, the method may further include the steps of (i) determining the
SOC of the first battery pack; and (ii) comparing the current SOC of the
first battery pack to a first preset minimum SOC to determine whether the
first battery pack needs immediate augmentation from the second battery
pack. Prior to utilizing the second battery pack, the method may further
comprise the step of comparing the current SOC of the second battery pack
to a preset minimum SOC, wherein use of the second battery pack is only
allowed if the current SOC of the second battery pack is greater than the
preset minimum SOC. The method may further comprise comparing the current
SOCs of both the first and second battery packs to preset minimums to
determine when vehicle operation must be terminated.

[0009] A further understanding of the nature and advantages of the present
invention may be realized by reference to the remaining portions of the
specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates the primary components of an electric vehicle
that utilizes both a metal-air battery pack and a conventional battery
pack;

[0016]FIG. 7 illustrates a methodology based on the processes shown in
FIGS. 3 and 5; and

[0017]FIG. 8 illustrates a methodology based on the processes shown in
FIGS. 4 and 6.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0018] In the following text, the terms "battery", "cell", and "battery
cell" may be used interchangeably. The term "battery pack" as used herein
refers to one or more individual batteries that are electrically
interconnected to achieve the desired voltage and capacity for a
particular application, the individual batteries typically contained
within a single piece or multi-piece housing. The terms "power system"
and "battery system" may be used interchangeably and as used herein refer
to an electrical energy storage system that has the capability to be
charged and discharged such as a battery or battery pack. The term
"electric vehicle" as used herein refers to either an all-electric
vehicle, also referred to as an EV, plug-in hybrid vehicles, also
referred to as a PHEV, or a hybrid vehicle (HEV), a hybrid vehicle
utilizing multiple propulsion sources one of which is an electric drive
system. It should be understood that identical element symbols used on
multiple figures refer to the same component, or components of equal
functionality. Additionally, the accompanying figures are only meant to
illustrate, not limit, the scope of the invention and should not be
considered to be to scale.

[0019] Given the high energy density and the large capacity-to-weight
ratio offered by metal-air cells, they are well suited for use in
electric vehicles. Due to their limited power density, however, their use
is most appropriate when combined with a more conventional power source,
such as a lithium ion battery pack. This aspect is illustrated in FIG. 1
which shows the primary components of an EV 100 that utilizes both a
metal-air battery pack 101 and a conventional, non-metal-air battery pack
103. As used herein, metal-air batteries refer to any cell that utilizes
oxygen as one of the electrodes and metal (e.g., zinc, aluminum,
magnesium, iron, lithium, vanadium, etc.) in the construction of the
other electrode. Conventional battery pack 103 utilizes non-metal-air
cells, and preferably ones that provide high power density, thus
providing a combined power source that achieves an optimal combination of
energy and power. Exemplary batteries used in conventional battery pack
103 include, but are not limited to, lithium ion (e.g., lithium iron
phosphate, lithium cobalt oxide, other lithium metal oxides, etc.),
lithium ion polymer, nickel metal hydride, nickel cadmium, nickel
hydrogen, nickel zinc, silver zinc, etc. In a preferred application,
battery packs 101 and 103 are coupled to one or more drive motors 105
that provide propulsion to one or more wheels of EV 100. A controller 107
optimizes the vehicle's hybrid power source, i.e., battery packs 101 and
103, in light of the current battery pack conditions (e.g.,
state-of-charge, temperature, etc.), preferred battery pack
charge/discharge conditions (e.g., state-of-charge, temperature range,
etc.), and the various operating conditions. Exemplary operating
conditions include those placed on the system by the user (e.g., speed,
acceleration, etc.), road conditions (e.g., uphill, downhill, etc.),
charging system (e.g., available power, available time for charging,
etc.), and environmental conditions (e.g., ambient temperature, humidity,
etc.).

[0020]FIG. 2 illustrates the basic methodology of the invention. As
shown, during the discharge cycle 201 one or both battery packs 101 and
103 provide energy to the intended application (e.g., propulsion,
cooling, auxiliary systems, etc.), the flow of energy represented by
paths 203/204. Similarly, during the charging cycle 205 one or both
battery packs 101 and 103 receive energy from a charging source, not
shown, the flow of energy represented by paths 207/208. The charging
source may be an external power source (e.g., power grid) or an internal
power source (e.g., regenerative system). Lastly, in some embodiments
energy may be transferred directly between battery packs 101 and 103 as
represented by energy flow pathway 209.

[0021] In accordance with the invention, and as illustrated in system 200,
controller 107 controls the flow of energy to and from both the metal-air
battery pack 101 and the non-metal-air battery pack 103. As described in
detail below, the methodology applied by controller 107 is based on the
input from a variety of sensors 211 as well as the current operating
conditions (e.g., temperature and state-of-charge (SOC), etc.) of both
battery packs.

[0022] The primary advantage of using two different types of battery
packs, and more specifically, a metal-air battery pack 101 and a
conventional, non-metal-air battery pack 103, is that the operational
characteristics of the two battery types are quite different. As a
result, an EV utilizing both battery types can be designed to take
advantage of the benefits of both battery types, while significantly
limiting the negative effects of either type.

[0023] While the specific operating requirements and characteristics of
the two battery packs will depend upon the particular chemistries of the
cells selected for each battery pack, the basic differences between the
two types are provided below, thus further clarifying how the present
invention utilizes both battery types to optimize operation of the
combined power source.

[0024] Energy Density--The energy density of the metal-air cells is very
high, even relative to high density non-metal-air cells such as
lithium-ion cells. In general, this is the result of the metal-air cells
utilizing oxygen, contained within the air, as one of the reactants, thus
reducing cell weight and increasing energy density. Accordingly, in
weight sensitive applications such as EVs, metal-air cells offer a
distinct advantage over non-metal-air cells in terms of energy density.

[0025] Power Density--The power density of a cell is determined by the
cell's reaction kinetics. Currently the chemistries, materials and
configurations used in metal-air cells provide a lower power density than
that achieved by many non-metal-air cells. While the lower power density
is adequate for many applications, it is lower than desired for more
demanding applications. As a result, by combining both cell types in a
single application as presently described, the high energy density,
moderate power density metal-air cells can provide a baseline power
source while the moderate energy density, high power density
non-metal-air cells can provide the necessary power for peak loads, for
example the loads that may be experienced during acceleration, high
speed, and hill climbing. Clearly the relative sizes allocated for each
battery type/pack within an EV depends upon the configuration and design
of the vehicle (i.e., vehicle weight, performance goals, etc.).

[0026] Optimal Charge/Discharge Temperatures--Temperature affects many
critical characteristics of battery operation regardless of the battery
type/chemistry. Exemplary characteristics affected by temperature include
cell voltage and discharge capacity, cell impedance, cell life,
non-recoverable capacity loss (at high temperatures), and charging
efficiency. While the preferred and optimal charge and discharge
characteristics depend upon the particular cell design, chemistry, and
reaction kinetics, in general metal-air cells may be charged and
discharged at lower temperatures than non-metal-air cells without unduly
affecting cell life and efficiency.

[0027] State-of-Charge (SOC)--The depth of discharge reached during the
discharge cycle, and the level that a cell is charged (up to 100%) during
the charge cycle, may dramatically affect the performance and life
characteristics of a cell. These characteristics are dependent upon cell
design and chemistry.

[0028] Recharge Characteristics--By definition a rechargeable battery is
rechargeable, however, the number of times that a cell may be recharged
without substantially affecting the capabilities and lifetime of the cell
vary greatly with cell design and chemistry. In general, however, current
state-of-the-art metal-air cells are not capable of being recharged as
many times as a non-metal-air cell without causing a significant
degradation in lifetime and capacity.

[0029] As noted above, the capabilities and lifetime of a rechargeable
battery are both affected by the number of times that the cell is charged
(i.e., charge cycles). Accordingly, in a preferred embodiment of the
invention, the dual battery pack arrangement is used to reduce the number
of times one, or both, battery packs are charged. As current metal-air
batteries are more susceptible to the effects of repeated charge cycles,
the present embodiment illustrates the use of the invention to minimize
the charge cycles of the metal-air cells relative to the charge cycles of
the non-metal-air cells. It should be understood, however, that the
invention may also be used to minimize the charge cycles of the
non-metal-air cells relative to the metal-air cells if, for example, at
some point the non-metal-air cells become more susceptible to the effects
of charging than the metal-air cells.

[0030]FIG. 3 illustrates a preferred embodiment of the invention
utilizing a first battery pack comprised of non-metal-air cell(s) and a
second battery pack comprised of metal-air cell(s). As shown, once
vehicle operation is initiated (step 301), the state-of-charge (SOC) of
non-metal-air battery pack 103 is determined (step 303). Note that in the
figures "non-metal-air" is abbreviated as "NMA" and "metal-air" is
abbreviated as "MA". Next, in step 305, it is determined whether or not
the current SOC is greater than a first preset SOC minimum
(SOC.sub.NMA-Min1). Preferably the first preset SOC minimum is set at the
absolute minimum SOC that the non-metal-air battery pack is allowed to
reach. Typically this minimum is selected to prevent irreparable damage
to the non-metal-air battery pack (e.g., 10% SOC, 5% SOC, 0% SOC or some
other value). As long as the SOC of the non-metal-air pack is above this
minimum (step 307), then the non-metal-air pack 103 is used to provide
operational power to the vehicle (step 309), thus not draining the
metal-air battery pack.

[0031] At step 311, the current SOC for the non-metal-air battery pack is
compared to a second preset minimum SOC (SOC.sub.NMA-Min2). Preferably
the second preset minimum is not the minimum allowable SOC for the
non-metal-air battery pack, rather the second preset minimum is set at a
level to ensure that vehicle performance is not affected while providing
sufficient time to take advantage of the vehicle having a second battery
pack, i.e., metal-air battery pack 101. For example, in one embodiment
the second preset minimum is set at 50% SOC; alternately, the preset
minimum is set at 40% SOC; alternately, the preset minimum is set at 30%
SOC; alternately, the preset minimum is set at 20% SOC. Other preset
minimums may be used. If the current SOC is greater than the second
preset (step 313), then the EV continues to utilize only the first
battery pack, e.g., non-metal-air battery pack 103, to provide power to
the drive system and the other vehicle subsystems.

[0032] During step 311, if controller 107 determines that the current SOC
of battery pack 103 is not greater than the second preset minimum (step
315), then the current SOC of metal-air battery pack 101 is determined
(step 317) and compared to a third preset minimum SOC, i.e.,
SOCMA-Min (step 319). Preferably the third preset minimum is set at
the absolute minimum SOC that the metal-air battery pack is allowed to
reach. Typically this minimum is selected to prevent irreparable damage
to the metal-air battery pack (e.g., 10% SOC, 5% SOC, 0% SOC or some
other value). As long as the SOC of the metal-air pack is above this
minimum (step 321), then the metal-air battery pack is used to charge the
non-metal-air battery pack 103 (step 323).

[0033] At step 325, the current SOC of the non-metal-air battery pack is
once again compared to the first preset minimum SOC. As long as the
current SOC is greater than the first preset minimum, the non-metal-air
battery pack is used to supply operational power to the EV (step 327). If
the non-metal-air battery pack was already being used to power the EV
(e.g., via step 309), then in step 327 utilization of this battery pack
continues.

[0034] Next the current SOC of the non-metal-air battery pack is compared
to a preset maximum SOC (step 329). Preferably the preset maximum is not
the maximum allowable SOC for the non-metal-air battery pack, rather the
preset maximum is the value for the non-metal-air SOC at which charging
from the metal-air pack is preferably terminated. For example, in one
embodiment the preset maximum is set at 90% SOC; alternately, the preset
maximum is set at 80% SOC; alternately, the preset maximum is set at 70%
SOC; alternately, the preset maximum is set at 60% SOC. Other preset
maximums may be used.

[0035] If controller 107 determines that the current SOC for the
non-metal-air battery pack is less than the preset maximum (step 331),
charging of the non-metal-air battery pack from the metal-air battery
pack continues. If controller 107 determines that the current SOC for the
non-metal-air battery pack is greater than the preset maximum (step 333),
charging is terminated (step 335) and vehicle operation continues with
only the first battery pack providing operational power to the vehicle.

[0036] At step 319, if the current SOC of the metal-air battery pack falls
below the third preset minimum SOC, i.e., SOCMA-Min (step 337),
charging is terminated (step 339). Even with the SOC of the metal-air
battery pack falling below the third preset minimum SOC, operation of the
vehicle may continue as long as the SOC of the non-metal-air battery pack
remains greater than the first preset minimum SOC (step 341). If the SOC
of the non-metal-air battery pack falls below the first preset minimum
SOC (step 343), then vehicle operation must be terminated (step 345). It
will be understood that the termination of vehicle operation will follow
a predefined procedure that may, for example, include low power warnings,
gradual reduction in power (e.g., decreased acceleration and top speed),
shut-down of non-essential vehicle systems (e.g., radio and interior
lighting) prior to shutting down essential vehicle systems, etc.

[0037] In the embodiment described above and illustrated in FIG. 3, the
second battery pack (e.g., the metal-air battery pack) is used to charge
the first battery pack (e.g., the non-metal-air battery pack) when the
SOC of the first battery pack falls below a preset value. In an alternate
embodiment illustrated in FIG. 4, when the SOC of the first battery pack
falls below the preset minimum (step 315), the second battery pack (e.g.,
metal-air battery pack 101) is used to augment the output from the
non-metal-air battery pack (step 401), assuming that the SOC of the
metal-air battery pack is greater than the preset minimum SOC as
determined in step 319. By augmenting the output from the first battery
pack, less drain is placed on it, thereby extending how long the first
battery pack may be used prior to reaching its minimum acceptable SOC. At
the same time, as the second pack (e.g., metal-air battery pack 103) is
only used when the SOC of the first battery pack falls below a preset
minimum, the second pack is protected from undergoing unnecessary charge
cycles.

[0038] In the embodiment illustrated in FIG. 4, once the current SOC of
the non-metal-air battery pack exceeds the preset maximum (step 333) or
when the current SOC of the metal-air battery pack falls below the third
preset minimum (step 337), use of the metal-air battery pack to augment
the output of the non-metal-air battery pack is terminated as illustrated
in steps 403 and 405, respectively.

[0039] In the embodiments illustrated in FIGS. 3 and 4 and described
above, the second battery pack, typically the metal-air battery pack, is
only used when the SOC of the first battery pack, typically the
non-metal-air battery pack, falls below a preset SOC value. As a result,
the second battery pack, typically the metal-air battery pack, is spared
from unnecessary charge cycles. FIGS. 5 and 6 illustrate modifications of
the embodiments illustrated in FIGS. 3 and 4, respectively, in which
whether or not the second battery pack is used depends upon a selection
made by the user (e.g., driver). More specifically, vehicle 100 includes
means for selecting a particular mode of operation, accessible by the
user, which allows the user to select between at least two modes of
operation; a normal range mode and an extended range mode. The mode
selector is integrated into the vehicle's user interface, for example
using a touch-sensitive screen or some form of switch (e.g., toggle
switch, push button switch, slide switch, rotating selector switch,
etc.). Alternately, the mode selection may be made in response to a
selection made by the user, for example, by the user setting a
destination in the navigation system that falls outside of the vehicle's
normal driving range, but within the vehicle's extended driving range.
Accordingly, it will be appreciated that the invention is not limited to
a specific means of selecting the operational mode of the vehicle.

[0040] As shown in FIG. 5, once vehicle operation is initiated (step 301)
the system determines whether or not the extended range mode has been
selected (step 501). As previously noted, the extended range mode may be
made using a mode selector or in response to another selection made by
the driver (e.g., destination entered into the navigation system). If the
extended range has not been selected (step 503), then the first battery
pack is used to supply all operational power to the vehicle, thereby
sparing the second battery pack from unnecessary use, and therefore
unnecessary charging cycles. Based on the current state-of-the-art, the
first battery pack is a conventional (i.e., non-metal-air) battery pack
and the second battery pack is a metal-air battery pack. This choice is
based on the achievable power density for each type of cell, as well as
the demonstrated sensitivity of each cell type to repeated
charge/discharge cycles.

[0041] If the normal range is selected, either via active selection or by
default, then the non-metal-air battery pack 103 is used to supply power
for all of the operational needs of the vehicle (step 505). If the
extended range is selected (step 507), then the non-metal-air battery
pack is used to supply power to the vehicle (step 509) and the metal-air
battery pack is used to charge the non-metal-air battery pack (step 511),
thereby maintaining the non-metal-air battery pack within a preferred SOC
range and extending its capabilities, and thus the vehicle's range.
Alternately, and as illustrated in FIG. 6 and described above relative to
FIG. 4, when the extended range is selected (step 507) the metal-air
battery pack is used to augment the output of the non-metal-air battery
pack (step 601), thereby extending the vehicle's range.

[0042] In an alternate embodiment, the ability to select a particular
operational mode (e.g., normal versus extended range) is combined with
the ability for the system to react to the SOC of the first battery pack
falling below a preset minimum. This combination of features allows the
user to pre-select an operational mode, and for the system to alter
operation based on the user's actual needs. Thus, for example, if a user
selects the normal operating mode based on the expected driving range,
but then unexpectedly exceeds the normal range, the system automatically
extends the driving range utilizing the second power source. FIG. 7
illustrates a preferred embodiment of this configuration, the illustrated
system including the attributes of the processes shown in FIGS. 3 and 5.
Similarly, the system illustrated in FIG. 8 combines the attributes of
the processes shown in FIGS. 4 and 6.

[0043] It will be appreciated that while the illustrated embodiments are
preferred, a variety of minor variations are envisioned that are clearly
within the scope of the invention. For example, the process illustrated
in FIG. 8 assumes that the capacity of the first battery pack, i.e., the
non-metal-air battery pack, is larger than that of the second battery
pack, i.e., the metal-air battery pack. As a result, in this embodiment
the SOC of the metal-air battery pack is expected to fall below its
minimum allowable SOC before the non-metal-air battery pack falls below
its minimum allowable SOC. Clearly the invention is not limited to this
configuration.

[0044] Additionally, while both the metal-air battery pack 101 and the
non-metal-air battery pack 103 are shown and described as singular packs,
it should be understood that one or both of these packs may be comprised
of multiple modules, and that the present invention is equally applicable
to such a configuration. The use of multiple modules (or mini-battery
packs) may be useful in distributing weight throughout EV 100, or to fit
into the physical constraints of the EV's chassis/body, and does not
impact the present invention.

[0045] As will be understood by those familiar with the art, the present
invention may be embodied in other specific forms without departing from
the spirit or essential characteristics thereof. For example, while the
illustrated embodiments assume the use of a non-metal-air battery pack as
the first battery pack and a metal-air battery pack as the second battery
pack, these battery types may be reversed, thus using the metal-air
battery pack as the first battery pack and the non-metal-air battery pack
as the second battery pack. Accordingly, the disclosures and descriptions
herein are intended to be illustrative, but not limiting, of the scope of
the invention which is set forth in the following claims.